Catheter ablation is a method of treating arrhythmia by inserting an ablation catheter into a cardiac chamber and cauterizing cardiac muscle tissue with electrodes attached to the distal end of the catheter. In that method, it is common to perform an electrophysiological examination using a catheter for measuring electric potential to determine the cautery site and confirm therapeutic effects. Catheters for measuring electric potential are constituted to comprise a plurality of electric potential-measuring electrodes, electric potential-measuring electrode leads connected to the electric potential-measuring electrodes, and an electric potential-measuring apparatus connector. A measurement of electric potential of cardiac muscle tissue allows for confirmation of the cauterized site and the cautery site.
In recent years, a balloon-tip ablation catheter in which a balloon attached at the distal side of a catheter is introduced percutaneously into inferior vena cava to reach the right atrium of the heart and the left atrium through the atrial septum and cardiac muscle tissue is cauterized by heating the balloon inflated there with a high-frequency current has been developed (JP 2002-78809 A and Japanese Patent No. 4062935) and become the mainstream of catheter ablation. Even in the treatment using a balloon-tip ablation catheter, an electrophysiological examination using a catheter for measuring electric potential is still required to determine the cautery site and confirmation of therapeutic effects, and thus a balloon-tip ablation catheter also having an electrophysiological examination function has also been reported (Japanese Patent No. 4417052).
However, the previously-reported conventional balloon-tip ablation catheters also having an electrophysiological examination function proved to be at high risk of causing, for example, thrombosis, excessive cauterization, and tissue perforation in an affected area because, when a balloon is heated by distributing high-frequency current between a return electrode outside the patient's body and a high-frequency current distributing electrode in the balloon, the high-frequency current is distributed also between the return electrode and electric potential-measuring electrodes, causing a phenomenon of abnormal heat generation at the electric potential-measuring electrodes.
On the other hand, when treatment is carried out with a catheter for measuring electric potential being provided separately from a balloon-tip ablation catheter to ensure patient safety, it is necessary to once evulse the balloon-tip ablation catheter from a patient and then again insert the catheter for measuring electric potential into a cardiac chamber to perform an electrophysiological examination, and a prolonged procedure time and the associated increased burden on physicians and patients are unavoidable.
Thus, it could be helpful to provide a highly safe catheter for measuring electric potential that can be inserted into a cardiac chamber together with a balloon-tip ablation catheter and is able to prevent abnormal heat generation at electric potential-measuring electrodes even when high-frequency current is distributed.